Hello again!
Facebook has never supported en_NZ.
We copied their public list (archive) in the plugin, and when your WordPress locale isn’t fully matched, it uses the first match (natural sort) based on the ISO language code instead, which in your case is en_GB.
Around mid-2017, they dropped that list. I just found a more recent page in another web archive from December 2018, which has this information hidden in the source of that page:
en_us, ca_es, cs_cz, cx_ph, cy_gb, da_dk, de_de, eu_es, en_pi, en_ud, ck_us, es_la, es_es, gn_py, fi_fi, fr_fr, gl_es, ht_ht, hu_hu, it_it, ja_jp, ko_kr, nb_no, nn_no, nl_nl, fy_nl, pl_pl, pt_br, pt_pt, ro_ro, ru_ru, sk_sk, sl_si, sv_se, th_th, tr_tr, ku_tr, zh_cn, zh_hk, zh_tw, fb_lt, af_za, sq_al, hy_am, az_az, be_by, bn_in, bs_ba, bg_bg, hr_hr, nl_be, en_gb, eo_eo, et_ee, fo_fo, fr_ca, ka_ge, el_gr, gu_in, hi_in, is_is, id_id, ga_ie, jv_id, kn_in, kk_kz, ky_kg, la_va, lv_lv, li_nl, lt_lt, mi_nz, mk_mk, mg_mg, ms_my, mt_mt, mr_in, mn_mn, ne_np, pa_in, rm_ch, sa_in, sr_rs, so_so, sw_ke, tl_ph, ta_in, tt_ru, te_in, ml_in, uk_ua, uz_uz, vi_vn, xh_za, zu_za, km_kh, tg_tj, ar_ar, he_il, ur_pk, fa_ir, sy_sy, yi_de, qc_gt, qu_pe, ay_bo, se_no, ps_af, tl_st, gx_gr, my_mm, qz_mm, or_in, si_lk, rw_rw, ak_gh, nd_zw, sn_zw, cb_iq, ha_ng, yo_ng, ja_ks, lg_ug, br_fr, zz_tr, tz_ma, co_fr, ig_ng, as_in, am_et, lo_la, ny_mw, wo_sn, ff_ng, sc_it, ln_cd, tk_tm, sz_pl, bp_in, ns_za, tn_bw, st_za, ts_za, ss_sz, ks_in, ve_za, nr_za, ik_us, su_id, om_et, em_zm, qr_gr, iu_ca, qk_dz, qv_it, qs_de, qb_de, qe_us, bv_de und qt_us
Again, no en_NZ… and they’ve since removed that list as well.
Now, the only public list is found in the link below–for Messenger–wherein en_NZ isn’t listed either:
https://developers.facebook.com/docs/messenger-platform/messenger-profile/supported-locales/
I’ll conduct further investigation on this matter, but so far I have nothing conclusive. I’ll have to test every WordPress locale against them and see if they’re accepted; this is tedious and ultimately redundant: I don’t believe this will affect sharing in any shape or form. NZ English looks like GB English, and Facebook doesn’t seem to close users off from different locales, regardless.
Nevertheless, you can overwrite the output, and see if Facebook accepts it via their Sharing Debugger:
add_filter( 'the_seo_framework_oglocale_output', function( $locale ) {
return 'en_NZ';
} );
I hope this explains the lot! ?? Have a beautiful day!